Temperature compensating grid



Sept. 27, 1960 G. L. RISHELL TEMPERATURE COMPENSATING GRID Filed Nov. 25, 1958 I NVEN TOR Crearge L. Ezblwll ATTORNEY Uite States Patent TEMPERATURE COMPENSATING GRID George L. Rishell, Emporium, Pa., assignor, by mesne assignments, to Sylvania Electric Products Inc, Wilmington, Del;, a corporation of Delaware Filed Nov. 25, 1958, Ser. No. 776,338

6 Claims. 01. 313350) peening, brazing or otherwise at each turn about the side rods. In another common form of grid, individual wires are stretched across the side rods and fastened at their end thereto.

When such grids are associated with a cathode and a made part of an electron tube the grid wires, which may be tungsten or molybdenum, expand unequally throughout the height of the grid and this expansion causes sagging of the grid laterals and with difierent degree along the height of the grid, impairing the operation of the tube. The expansion of the lateral wires is due to the heat radiated from other electrodes and electron bombardment of the lateral wires as the electron stream flows from cathodes to anode, the greatest heat being near the longitudinal center of the grid.

It is an object of this invention to provide a grid electrode that retains the spacing of the lateral wires substantially constant throughout the operating range of temperature of an electron tube.

Other objects will become apparent upon consideration of the following specification when taken in conjunction with the accompanying drawing in which:

Fig. l is an elevation of a grid electrode according to this invention with the siderods extending through apertures in insulating spacer plates and with reinforcing bars or straps spanning the siderods.

Fig. 2 is cross sectional view of a siderod of the grid elect-rode taken along the line 22 of Fig. 1, showing the bimetallic structure thereof.

Fig. 3 is a sectional longitudinal view of a portion of a bimetallic siderod taken along line 33 of Fig. 2.

Fig. 4 is an elevation of a grid electrode according to this invention, without straps joining the siderods, and having a uniform pitch winding as distinguished from the variable pitch winding illustrated in Fig. 1.

Fig. 5 illustrates a variation of the invention wherein the cross section of the siderods is semicircular and Fig. 6 illustrates another cross sectional form of siderod.

Fig. 1 illustrates a grid having a plurality of lateral wires 10 supported by bimetallic siderods 12 and 14. The siderods are rigidly joined by straps 16 and 18 to form a rigid frame and extend snugly through apertures in insulating spacers 20 and 22. Other electrodes have been omitted from the drawings because their specific constructions are not directly related to the invention.

During operation of the tube, heat is radiated from cathode to grid and simultaneously the grid lateral wires are bombarded by electrons as the electron stream flows from cathode to anode. The siderods become heated as well as the grid laterals since heat is conducted from the lateral wires to the siderods. The lateral wires expand when they are heated and when expanded excessively they sag, and distort the lateral wire spacing.

The grid electrode made according to this invention has siderods that change from straight supports to curved or bowed supports when they are heated, as indicated by the dotted curved lines in Figs. 1 and 4, to overcome the sagging of the grid lateral wires.

In accordance with this invention one or both of the grid siderods is made of bimetallic elements secured together to cause the siderod or rods to bow in the directions indicated in the drawing when they are heated, preferably to a degree commensurate with the sagging of the grid laterals to take up the slack therein. If, in manufacture, the bowing is made greater than the initial sagging of the grid laterals, the grid laterals will be permanently stretched as the grid siderods bow, imparting a permanent minimum length to the span of the grid laterals between the siderods. When cold they are shortened and the siderods are straight. Subsequent heatings of the tube to substantially the same temperature will maintain the grid laterals taut as the grid laterals are lengthened and the siderods bow more and more until the parts are brought to their operating temperatures.

In Figs. 1 and 4, the bowing of the grid siderods, to an exaggerated degree, is indicated in dotted lines. In practice the metal of the portions 24 and 26, which may be brazed to each other, are selected so that the portion 26, most removed from the longitudinal center of the grid, has a higher coefficient of expansion with heat than the portion 24, as for example iron or steel for the element 24 and copper or an alloy with a high percentage of copper for the element 26.

In Fig. 2 the bimetallic siderod is shown as elliptical, but the particular shape of siderod is unimportant so long as it bows to a suffioient degree to take up the slack in the grid laterals as they expand under heat. Thus, if desired, the outline of the two metals 28 and 30 corresponding to the metals 24 and 26, may be semicircular as in Fig. 5 or as shown in Fig. 6, the iron member 32 may be rectangular in cross section while the copper member 34 may be semicircular in cross section. Since the'heating is greater at the center of a grid than at the ends, the securement of the ends of the grid siderods in the spacers is most effective for securing the proper bowing action of the grid siderods.

The bimetallic siderods may be employed either with a grid wound with non-uniform pitch as in Fig. 1 or with uniform pitch as in Fig. 4. While it is most desirable for frame rigidity to employ the straps 16 and 18 shown in Fig. 1, nevertheless good results are obtained where such straps are not employed, as in Fig. 4.

Having thus described the invention what is claimed is:

1. A grid composed of grid laterals and grid siderods, with the grid laterals arranged transverse to the siderods, the grid laterals being secured to the siderods and each of the siderods being formed of thermionic bimetallic elements contiguous throughout their lengths.

2. An elongated grid composed of grid laterals and elongated grid siderods with the ends of the laterals fastened to the siderods, at least one of the siderods being formed of thermionic bimetallic elements fastened together throughout their lengths with the element of greater coeificien-t of expansion farthest from the longitudinal center of the grid. I

3. An elongated grid comprised of a grid wire wound about a pair of grid siderods to form grid laterals with the turns of the wire fastened to the siderods, at least one of said siderods being of two elements having difi'erent coefiicients of expansion fastened together throughout their lengths with the element of higher coefiicient of expansion farthest removed from the longitudinal center of the grid.

4. An elongated grid comprised of a grid Wire Wound about a pair of grid siderods to form grid laterals with the turns of the Wire fastened to the siderods, at least one of said siderods being of two elements having different coefficients of expansion fastened together throughout their lengths with the element of higher coefli'eient of expansion farthest removed from the longitudinal center of the grid, and insulating spacers snugly receiving the ends of the siderods.

5. An elongated grid comprised of a grid wire wound about a pair of grid siderods to form grid laterals with the turns of the wire fastened to the siderods, at least one of said siderods being of thermionic bimetallic elements with the element of higher coefiicient of expansion farthest removed from the longitudinal center of the grid, and straps bridging the siderods and fastened thereto above and below the winding.

6. An elongated grid comprised of a grid Wire wound about a pair of grid siderodsto for-m grid laterals with the turns of the wire fastened to the siderods, at least one of said siderods being of thermionic bimetallic elements with the element of higher coefiieient of expans/ion farthest removed from the longitudinal center of the grid, strap-s bridging tthetsiderods and fastened thereto above and. below the Winding and insulating spacers snugly receivinggt he' ends ofthe siderods.

References Cited the file of this patent "UNITED STATES PATENTS 2,495,259 Jackson -2 Jan. 24, 1950 2,599,395 Kohl June 3, 1952 2,832,911 Van Velzer Apr. 29, 1958 2,897,395 Miller July 28, 1959 

